Magnavox 42mf531d/37 trouble.

[Sean9275]

I have acquired a Magnavox 42mf531d 37 that has no picture. Upon turning the tv on, after a brief moment, the screen flashes dark gray/black and then nothing. The LED on the switch illuminates steady green. The audio, (I am told by previous owner,) works normally.

After researching this condition the capacitors became the prime suspects. Upon visual inspection, there appeared to be no obvious defect with any capacitors on the power board or any other board for that matter. Based on a search of this model tv and similar models on this site, I proceeded to test the components on the boards according to those previous posts.

To the best of my knowledge, the tv was manufactured in early 2007 with components from late 2006.

This is not my area of expertise, I know just enough to be dangerous.

Any help would be greatly appreciated.

[PlainBill]

Re: Magnavox 42mf531d/37 trouble.

Is there any sign of backlights? Have you verified sound? Have you checked if a faint image is visible if you shine a bright light on the screen?

PlainBill

[Sean9275]

Re: Magnavox 42mf531d/37 trouble.

I just verified sound from a dvd player into av2. No faint image with a bright flashlight aimed at screen. The menu bar pops up on power on and faintly flickers before the whole screen goes dark. No image during any of this sequence. I'm not sure how to check for backlights, nothing around the perimeter of the screen. There is some visible light coming from inside the back cover of the tv. It is green, I assume an LED or two, (I know what happens when I assume.)

Where to go from here?
Thanks,
Sean

[tom66]

Re: Magnavox 42mf531d/37 trouble.

Is the back of the TV lit up white?

Post a picture of the inverter, it's usually on the left or right hand side of the TV. Sometimes there are two.

[Sean9275]

Re: Magnavox 42mf531d/37 trouble.

The back of the tv is not lit up. Here is a photo of each of the inverters.

[tom66]

Re: Magnavox 42mf531d/37 trouble.

Ah! Darfon inverters. Often fail, dead easy to repair . Repaired two previously. Usually one of the transformers fails open circuit.

While the TV is off completely (unplugged) use your multimeter to measure the resistance between each of the two pins I have highlighted for every transformer on both the master and slave boards. Use the 20k range.

All but one will measure nearly the same value. The one which measures significantly different (often open circuit or "1 ." has failed. Note these values down and post here.

A new transformer is about $10 and it would be rare for more than one to have failed. Report back the part # on the transformer (looks like 4004?) so we can help you locate a good part.

Removing the original transformer requires a bit of soldering experience to do it properly (for example, using wick) but I've done it before by just heating up each pad and using the soldering iron to pull each pin off the board... worked for me... Putting a new one on is much easier.

You could also of course go for the approach of getting a new inverter but that often costs a lot more than a transformer.

[Sean9275]

Re: Magnavox 42mf531d/37 trouble.

Starting from the bottom of each board:
RH LFT
1) 4.16 11) 4.14
2) 4.12 12) 4.16
3) 4.11 13) 4.13
4) 4.11 14) 4.12
5) 4.12 15) 4.13
6) 4.08 16) 4.12
7) 4.11 17) 4.13
8) 4.09 18) 4.12
9) 4.11 19) 4.15
10) OL 20) 4.10

The part number on #10 reads 4004Q648 139<GP>.
The picture is of #1 for reference.

[tom66]

Re: Magnavox 42mf531d/37 trouble.

Starting from the bottom of each board:
RH LFT
1) 4.16 11) 4.14
2) 4.12 12) 4.16
3) 4.11 13) 4.13
4) 4.11 14) 4.12
5) 4.12 15) 4.13
6) 4.08 16) 4.12
7) 4.11 17) 4.13
8) 4.09 18) 4.12
9) 4.11 19) 4.15
10) OL 20) 4.10

The part number on #10 reads 4004Q648 139<GP>.
The picture is of #1 for reference.

So #10 has failed.

Replacement: http://www.ebay.com/itm/Inverter-Tra...item2eb97bce20

This is a closer match but more expensive: http://www.ebay.com/itm/4004Q-invert...item2310bd79f1

Often only the first three digits matter, so you could even use a 4009, but I wouldn't guarantee it.

[PlainBill]

Re: Magnavox 42mf531d/37 trouble.

So #10 has failed.

Replacement: http://www.ebay.com/itm/Inverter-Tra...item2eb97bce20

This is a closer match but more expensive: http://www.ebay.com/itm/4004Q-invert...item2310bd79f1

Often only the first three digits matter, so you could even use a 4009, but I wouldn't guarantee it.

The first four digits are significant; the rest are production lots or date codes. Don't try substituting a different number. Some sellers indicate the 4006 and 4009 are interchangeable, but the turns ratios are different.

PlainBill

[Sean9275]

Re: Magnavox 42mf531d/37 trouble.

I've ordered the first one as it will be here several weeks sooner. I'll post the results when I have news to report.
Thanks for the input
Sean9275

[tom66]

Re: Magnavox 42mf531d/37 trouble.

The first four digits are significant; the rest are production lots or date codes. Don't try substituting a different number. Some sellers indicate the 4006 and 4009 are interchangeable, but the turns ratios are different.

PlainBill

Do you happen to have any datasheets for cross referencing these part #s? I've always been curious about the part numberings...

[tom66]

Re: Magnavox 42mf531d/37 trouble.

One thing: When you replace the transfomer make sure the white dot is in the same position as the others or it won't work.

[retiredcaps]

Re: Magnavox 42mf531d/37 trouble.

This is a closer match but more expensive:

I remember seeing something on http://www.alibaba.com regarding these types of transformers.

The markup is huge for these ebay sellers. They buy 100 at a time for 50 cents each and resell them for $10 or more.

[PlainBill]

Re: Magnavox 42mf531d/37 trouble.

Do you happen to have any datasheets for cross referencing these part #s? I've always been curious about the part numberings...

Very limited datasheets here (click on the .pdf link).

PlainBill

[Sean9275]

Re: Magnavox 42mf531d/37 trouble.

I've replaced the defective 4004Q648 139<GP> transformer with the ebay 4004L530008(GP) transformer. The tv still goes to black after a second, however the faint flicker before it turns black is gone.

My soldering gun may have been overkill for this job. Consequently, during the removal process, the small pad under pin 7 was liberated from the board. I did retrive it from molten solder, but was unable to attach it back to the board. Then I lost the little thing as I proceeded downhill at an increasing rate. I could see no visible circuit underlying pin 7 in that location or any of the adjacent transformers. Also it appears pin 6 has no circuit associated with it. Thinking I had nothing to loose, I proceeded to solder the replacement transformer in place and build up some solder on pin 7 and hoped for the best. Reassemble tv, fail. Moving right along, I tested the replacement transformer as well as several others (both the defective one and a couple good ones still on the board).

DMM set to 20k ohms
Column 1 Terminals
Column 2 Replacement: 4004530008(GP)
Column 3 Other one in picture: 4004Q648 173<GP>
Column 4 Defective 4004Q648 139<GP>

8-5 4.29 4.10 O.L.
1-8 1.47 1.35 O.L.
4-5 1.48 1.36 1.35
1-5 2.82 2.72 O.L.
4-8 2.82 2.71 O.L.
2-7 0.01 O.L. O.L.
3-6 0.01 O.L. O.L.


One other difference between the replacement transformer and the replaced is the plastic alignment nubs on the underside. I used the soldering gun to melt the one that was preventing flush mounting. In retrospect, was this the first clue of something wrong?

What is the next step?
Thanks for all the help so far.